A fluid reforming apparatus of the present invention includes: a flow channel (30) in which a catalyst (1) is fixed to an inner wall; a fluid heating device (40) which heats a fluid to be reformed by the catalyst (1) and / or heats the catalyst (1) in the flow channel (30); catalyst temperature measuring devices (51, 52, 53, 54) which measure temperatures of the catalyst (1); and a pressure control device (10, 20, 60) which controls a pressure of the fluid in the flow channel so that the fluid can have a target pressure. The pressure control device (10, 20, 60) increases the target pressure when a difference between the temperatures of the catalyst (1) in a flow direction of the fluid exceeds a predetermined value during a period while the fluid in the flow channel (30) is being heated up to a target temperature.